1. Field of Invention
The present invention relates to an air bag apparatus for a passenger seat having an air bag door deployably disposed in a passenger seat-side upper portion of an instrument panel and facing a windshield pane, an air bag case supported by a vehicle body component member and housing an inflator and a bag, and a restriction device connecting the air bag door to the air bag case or the vehicle body component member so as to restrict the deployment angle of the air bag door.
2. Description of Related Art
In a so-called dashboard-type air bag apparatus for a passenger seat, an air bag door is normally deployed toward the windshield pane in a single-hinged manner. For the purpose of preventing interference between the air bag door and the windshield pane, the use of a strap has been proposed. Such an air bag construction employing a strap is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 7-323800, U.S. Pat. Nos. 4,911,471 and 5,385,366, and will be briefly described below.
Referring to FIGS. 17 and 18, a conventional air bag apparatus 170 for a passenger seat is disposed in a passenger seat-side upper portion of an instrument panel 172. The air bag apparatus 170 includes an air bag unit 174 supported by a vehicle body component member, and an air bag door 178 fixed to the air bag unit 174 by rivets 176 so as to confine the air bag unit 174.
The air bag unit 174 has a tray-shaped air bag case 180 in which an inflator 182 and a folded bag 184 are disposed. A hinge 186 is formed in a reverse (interior) surface of the air bag door 178, more specifically, in a portion of the air bag door 178 near a forward end thereof, by reducing the wall thickness of the portion. A breakable portion 190 is formed near a rearward end and opposite side ends of the air bag door 178, thus extending in a generally squared "U" shape, whereby the air bag door 178 can be deployed pivotally about the hinge 186.
The air bag door 178 is formed from urethane foam. Resin-made reinforcing meshes 192 formed of, for example, polyester yarns, are embedded in the air bag door 178 by insert molding, but not in the breakable portion 190. A strap 194 extends behind the air bag door 178 substantially in a transverse direction relative to the vehicle, near and along a front-side extension of the breakable portion 190, with an intermediate portion of the strap 194 sewed to a portion with an embedded reinforcing mesh 192 near the front extension of the breakable portion 190. Opposite end portions of the strap 194 are fastened to side flange portions of the air bag case 180, using retainers 196 and bolts, so that portions of the strap 194 between the sewed intermediate portion and the bolt-fastened end portions are left slack or bent.
If a predetermined high load is applied to a front portion of the vehicle body, the inflator 182 ejects gas to expand the bag 184. Due to the expanding pressure from the bag 184, the air bag door 178 is broken along the breakable portion 190, and deployed toward the windshield pane 188 pivotally about the hinge 186. As the air bag door 178 is thus deployed, the slack or bent portions of the strap 194 become extended and taut, thereby restricting the deployment angle of the air bag door 178. The interference between the air bag door 178 and the windshield pane 188 can thus be prevented.
However, the resin-made strap 194 degrades due to an influence of a component material of the foam layer (urethane foam) of the air bag door 178 (more specifically, so-called amine attack wherein the polyester yams of the strap are hydrolyzed by urethane in contact and thus degrade over time).